Insulated electrical conductor and method of producing same



Patented Aug. 17,1954

UN STATES tarsus orries.

INSUIJATEDLELEGTRICAL CONDUCTOR. AND

METHODiOFPRODUCING SAME JbhnJT. Goodwin, Midland; Mich, assignor, to Dow Corning Corporation, Midland; Micln, a.

corporation of Michigan Nb Drawing: Application May 31, .1951; Serial No. 229,259'

Ihe present inventiontrelates to new and im proved alkyd resins and,,inparticular, to..a1kyd.

resins ofthermal stability far greater than any heretofore knownalkyd-resins.

Alkyd resinsain general are prepared. by the interaction of a. polybasie, acid and; a polyhydrie alcohol. The-polyhydric alcohol employed is, in

general, .glycerine which, having three hydroxyl. radicals,,makesvpossible'thecross linking of the polymer to forma resin. The-polybasic acid em,- ployed in the preparation of allrydsisphthalic anhydride. While other polybasic acids have been mentioned as beingequivalent to phthalic anhydride ororthophthalic acid; the: methods which have beendescribedfor the-preparation of alkyd resins: are-:- unsuitable for. i the preparation of resins from; certain polybasic acids. I1'l\p2LI'- ticular, these methods are unsuitable for. the preparation of alkyd type resins from terepha thalic; acid and isophthalic acid.

. azdiesterofthe tereandiisophthalio acid.

Resins in. accordance with the present: inven tion' are polyesters of a polyhasic acid: of the group consisting of terephthalic aoid and isophthalic acid) and of: apolyhydric alcohol. of the group consisting of glycerine and pentaerythritol.

In accordance with a specifio pref rred embodiment of the resinsof. the, present invention, a

resin as above stated modification.

Further, the present invention relates to a specific preferred method for the preparation of resins as above-stated: the, use of diesters oi the dibasic acids and. the interaction, of these esters with thepolyhydric alcoholsby ester interchange. For the preparation of'the .si1iconemodified resins; thegproduct' of" the ester interchange may-be reacted' with a, suitable organic silane;

contains organic silane The resins hereofcontainpolymer.units derived from" the polyhydric alcohol and polymer units.

derived. from the dibasio acid in such, relative proportion as to reflecta ratio ofbetween 0.9 and thydroxyl'radicals per carboxy radical; Thus, the. ratio of the. sum of the hydroxyls. plus the ester linkages inthe resin to the sumof the .oar..-

boxy radicals plus the ester linkagesis between 0.9 to 1 and to 1.

From the ratios stated; it is obvious that. there may be a slight. excess-oi acid radicalsoven the alcohol'hydroxylradicals in the resin.-. Alternae tively, the alcohol may, be, employed in quantity such that there are four alcoholic hydroxyl radicalsper carboxy radical; in'which oase-thereare three hydroxyi radieals forevery ester linkage.-

Considerable difficulty: is encountered in' the preparation. of resins which" conformv to the present invention, particularly dueeto;the-insolubility and high melting' pointl of, te'rephthalic acid.

Furthermore, when. pentaerythritol is employed.

for theprocess, difficulties are encountered in particular withrespeet: to solubility thereof One suitable method; for the preparation .ofi resins in accordance herewithis by heating a mechanical mixture of: the polybasio acid and the polyhydric alcohol; Partioularlywith glycerinaqitq is pos sible to) obtain some esterification of the slurry. Garewmust. be-employed during; heating to avoid local. overheating: of: the reaction mixture.-

The preferred method-tin;aceordance 'with the present invention. involves thee employment,- or

ester'emplayed" is a dialkyl. terephthalate or isophthalate such; .for'exarnple, as 1 a diesten formed from; an; alcohol: from methanol to octanol, inclusive; Higherwboiling alcohols may be usedzfor the preparation: of a the ester; However, these are lessrdesired, particularly. due to the lower. volatility of the alcohol producediin'. the ester interchange. In. accordance With this method, the dialkyl ester of the t'ereor isophthalic acid? is heated with glycerineor. pentaerythritoli During the heating the equivalent alcohol-is liberated andis re moved. Thismethod is quiteadvantageousin comparisonwithithe direct heating of the dibasic acidwandithepolyhydric alcohol, due to tlie much lower melting point of 'the dialkoxy esters of the acids in. question; i

Other methods for the preparation'of the resins hereof may be employedii. desired.

In those resins which are silane modified, the resins contain condensedl therein units of" the average general formula R sh) The phenylmethyldiethoxysilane,

esters of the type described in which there is an excess of hydroxyl radicals bonded to the polyhydric alcohol residues or units. The modifying silane is bonded thereto through an SiOC linkage. The silane may be used in amount up to an amount equivalent to the residual hydroxyls. Thus, the siloxy may be present in amount up to sufiicient that all alcoholic hydroxyls are esterified either with carboxy substituents or with siloxy substituents.

Thus, if one mole of glycerine is employed, this provides three hydroxyl radicals. If one mole of terephthalic acid is employed, this provides two carboxy radicals. If phenylmethyldiethoxysilane is employed for silane modification, it may be employed up to one-half mole, whereby to provide two bonds from silicon available for condensation with hydroxyls. Thus, there are three polyhydric alcohol hydroxyls, which limits the amount of the silane employed to the amount stated, due to two of the hydroxyls being esterified with the terephthalic acid.

When the preferred method for preparing the resins as above described is employed and it is desired to modify the resin with siloxy substituents, a silane is reacted by heating it with the glyceryl ester. The silane employed is of the general formula RnSiX4n, in which R represents alkyl, aryl or aryloxy or mixtures thereof, X represents alkoxy, aryloxy or halogen, and n has a value from to 3, inclusive. The silane may be employed in amount up to that amount equivalent to the number of free alcoholic hydroxyls remaining in the glyceryl ester.

Resins in accordance with the present invention are of exceedingly unusual properties for alkyd resins. When cured, they are hard, tough and flexible. Accordingly, they are of utility as magnet wire enamel and for panel coating on automobiles and the like. Further, due to their exceptional heat stability far and above heretofore known alkyd resins, they are useful for panel coating of articles operating at exceptionally high temperatures, as for example, furnaces, stoves and smokestacks. To obtain the maximum benefit of this invention, it is necessary that they be cured at a temperature of at least 200 C., thereby eliminating brittleness. The time Varies with the temperature and thickness of the resin. Thus, at 200 C. it may take one hour or more, while at 150 C. one minute of annealing is usually sufficient. At 500 to 600 C. very short times are used.

Example 1 Glycerine in amount of 92 grams was mixed with 83.05 grams of terephthalic acid, and the mixture was heated. Droplets of water started to ing and panel coating. The silane modification effects some change of the properties of the resin.

Example 2 A mixture of 41.4 grams of glycerine containing 4.85 per cent water and grams of diethylterephthalate was heatedwith 0.18 gram of zinc oxide and 0.18 gram of calcium oxide. The mixture was heated for four hours at a temperature of 194 C. with agitation and with carbon dioxide bubbling through the mixture. During this heating 17 grams of ethanol was removed by distillation with the carbon dioxide. The resin so produced was a viscous, cloudy tan fluid which could be set to a solid upon heating as a film. To the resin so prepared 94.5 grams of phenylmethyldiethoxysilane were added. The addition was made at a temperature of 90 C. The mixture was heated for thirty-five minutes at top temperature of 170 C., allowing volatile material to escape. During the ensuing fifteen minutes the temperature was raised to 182 C. By this time the resin was highly viscous. 80 grams of cyclohexanone were added. While the resin was poorly soluble, most of it was dissolved in the cyclohexanone by stirring. The undissolved resin was removed by filtration, to give a clear brown resin solution. The resin was employed to coat a panel and was found to cure in one to two hours at 135 C. to a clear hard film. The weight loss a on heating the resin for three hours at 200 C.

the reaction mixture throughout the heating periods. 190 grams of cyclohexanone was added and the solution filtered to remove the product was found to be 6.9 per cent.

Example 3 46 grams of anhydrous glycerine and grams of isophthalic acid and 200 grams of butyl Car- 1 bitol acetate were mixed and heatedat 240 C.

Example 4 A mixture of 92 grams of anhydrous glycerine, 83 grams of terephthalic acid and '70 grams of diethyl Carbitol was mixed and heated at to 215 C. for nine hours. During this time 20 ml. of water was removed. The reaction mixture was cooled to 40 C., and 100 grams more of diethyl Carbitol was added. The solution was stirred as a mixture of 163 grams of phenylmethyldichlorosilane and 20.5 grams of phenyltrichlorosilane was added. Hydrogen chloride was evolved. After standing over night, the mixture was heated up to C. for ten hours. More HCl came off as the viscosity of this material gradually increased. At the end of the heating period, 200 grams cyclohexanone was added. The resin solution was coated on copper wire as in Example 3, and the resulting film had an initial scrape hardness of 14 ounces, which dropped to 12 ounces after twenty-four hours at 35 C. in 100 per cent relative humidity.

Ewample 5 72.4 grams of pentaerythritol, 83 grams of terephthalic acid and 100 grams of dimethylformamide were mixed and heated from. 180 to 215 C. for twenty-one hours. The mixture was cooled to 90 C. and 148 grams of a partially hydrolyzed phenylmethylsiloxane containing 39.7 per cent by weight silicon-bonded isopropoxy groups was added. The temperature was then raised to 150 C. over a period of four hours, during which time 46 grams of isopropanol was removed. The resin was then cooled, and 400 grams of dimethylformamide was added. The resulting solution was filtered and was coated on copper wire, which was then passed through a tower at the rate of 5 feet per minute and heated at a temperature of 420 C. The resulting film had an initial scrape of 18 ounces, and after twenty-four hours at 35 C. at 100 per cent relative humidity, the scrape was 18 ounces.

Example 6 92 grams of anhydrous glycerine, 211 grams of terephthalic acid and 200 grams of butyl Carbitol acetate were heated at 240 C. for four and one-half hours. The solution was cooled to 180 C., and 55.5 grams of tetracresoxysilane was added. The mixture was heated to 245 C. for four hours. During this time 12 ml. of cresol was removed. The resulting resin was coated on copper wire by the method of Example 3, and the resulting coat had an initial scrape of 20 ounces. This value was maintained after twenty-four hours at 100 per cent relative humidity and after one hour in toluene.

Example 7 92 grams of anhydrous glycerine and 83 grams of terephthalic acid were mixed with 200 grams of butyl Carbitol acetate and heated at a temperature of 238 to 249 C. for one hour. The material was placed on an aluminum dish and heated at 250 C. for one and one-half hours to give a flexible tough film. The material coated satisfactorily on bare copper wire in accordance with the procedure in Example 3.

That which is claimed is:

1. A method of preparing an electrical conductor for use in electrical equipment which comprises coating the conductor with a solution of a modified polyester resin of an alcohol selected from the group consisting of glycerine and pentaerythritol, an acid selected from the group consisting of terephthalic and isophthalic acids and dialkyl esters of said acids, and a silane of the formula RnsiXr-n in which R is of the group consisting of alkyl, aryl, and aryloxy radicals, X is of the group consisting of alkoxy, aryloxy, and halogen, and n has a value of from 0 to 3, in said modified polyester resin the acid and silane being present in amount equivalent to the alcohol, and thereafter heating the conductor at a temperature of at least 200 C.

2. An article of manufacture comprising an electrical conductor having thereon a resinous coating which was cured at a temperature of at least 200 C., said coating having a scrape hardness upwards of 18 ounces and maintaining its hardness essentially unchanged after being subjected for 24 hours to an atmosphere of per cent relative humidity at 25 C. and after being immersed in toluene for one hour at 25 C., said coating having exceptional heat stability and being composed essentially of the reaction product of an alcohol selected from the group consisting of glycerine and pentaerythri'tol, an acid selected from the group consisting of terephthalic and isophthalic acids and dialkyl esters of said acids and a silane of the formula RnsiX4-n in which R is selected from the group consisting of alkyl, aryl, and aryloxy radicals, X is of the group consisting of alkoxy, aryloxy, and halogen and n has a value from 0 to 2, in said reaction product the acid and silane being present in amount equivalent to the alcohol.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,048,799 Lawson July 28, 1936 2,258,221 Rochow Oct. 7, 1941 2,340,109 DAlelio Jan. 25, 1944 2,465,319 Whinfield et al. Mar. 22, 1949 FOREIGN PATENTS Number Country Date 622,671 Great Britain May 5, 1949 650,247 Great Britain Feb. 21, 1951 OTHER REFERENCES Hovey et a1.: Paint Oil and Chem. Review, January 18, 1940, pages 9, 37, 38, 42. 

1. A METHOD OF PREPARING AN ELECTRICAL CONDUCTOR FOR USE IN ELECTRICAL EQUIPMENT WHICH COMPRISES COATING THE CONDUCTOR WITH A SOLUTION OF A MODIFIED POLYESTER RESIN OF AN ALCOHOL SELECTED FROM THE GROUP CONSISTING OF GLYCERINE AND PENTAERYTHRITOL, AN ACID SELECTED FROM THE GROUP CONSISTING OF TEREPHTHALIC AND ISOPHTHALIC ACIDS AND DIALKYL ESTERS OF SAID ACIDS, AND A SILANE OF THE FORMULA RNSIX4-N IS WHICH R IS OF THE GROUP CONSISTING OF ALKYL, ARYL, AND ARYLOXY RADICALS, X IS OF THE GROUP CONSISTING OF ALKOXY, ARYLOXY AND HALOGEN, AND N HAS A VALUE OF FROM 0 TO 3, IN SAID MODIFIED POLYESTER RESIN THE ACID AND SILANE BEING PRESENT IN AMOUNT EQUIVALENT TO THE ALCOHOL, AND THEREAFTER HEATING THE CONDUCTOR AT A TEMPERATURE OF AT LEAST 200* C. 